I have a crabapple tree that is at least 15 years old. Last year it got apple scab but it was too late to treat it. We completely forgot about it and again this year we are having problems. Is there anything we can do at this time or do we need to wait until next spring to treat the tree? I read about spraying the tree but it is a very tall mature tree.
Crabapples are subject to several fungal diseases. The best recommendation is to plant resistant varieties. It is too late to spray a fungicide this year. Rake and destroy any fallen leaves and fruit. If you want to spray, it will have to be next season. See the link from our website http://extension.umd.edu/hgic/scab-apples-trees
and Penn State on http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/crabapple-diseases